I seem to remember someone recently making a post about
how their transmission was jumping out of third gear.
I was just reading through a copy of the Toronto Triumph club magazine,
and noticed an article on Transmission Lubricants. The author states that
a group of his friends experienced this problem in TRs in which they had
used synthetic gear oils. They performed experiments and tore down a
transmission to check the problem.
After reverting to standard 80-90 gear oil, the problem was gone. They
also stated that synthetic gear oil caused problems getting into first
They recommend 20-50 engine oil in the OD equipped units.
I'm no expert, etc., just passing on what I read.